P. Ya. Ufimtsev

Bio: P. Ya. Ufimtsev is an academic researcher from University of California, Los Angeles. The author has contributed to research in topics: Physical optics & Diffraction. The author has an hindex of 6, co-authored 9 publications receiving 240 citations. Previous affiliations of P. Ya. Ufimtsev include Northrop Grumman Corporation.

Elementary Edge Waves and the Physical Theory of Diffraction

Abstract: A more general and rigorous form of the physical theory of diffraction (PTD) is presented. This theory is concerned with the field scattered by perfectly conducting bodies whose surfaces have sharp edges and whose linear dimensions and curvature radii are large in comparison with a wavelength. The PTD proposed here is based on the conception of elementary edge waves (EEWs). These are the waves scattered by the vicinity of an edge infinitesimal element. Their high-frequency asymptotics are given. Various definitions of EEWs (Maggi, Bateman, Rubinowicz, Mitzner, Michaeli) are discussed. Total edge waves (TEWs) scattered by the whole edge are found to be a linear superposition of all EEWs. PTD enables one to determine correctly the first (leading) term in the high-frequency asymptotic expansions for primary and multiple TEWs both in ray regions and diffraction regions such as caustics, shadow boundaries, and focal lines. Some examples of these asymptotics are given. The connection of PTD with other ...

On the Modified Theory of Physical Optics

Abstract: Basic features of the modified theory of physical optics (MTPO) are discussed on the example of scattering at perfectly reflecting half-planes and wedges. It is shown that violations of the geometrical optics (GO), introduced in this technique, result in the MTPO solutions which do not satisfy the Helmholtz equation. They are incorrect at a finite distance from a scattering object; however it can be considered as sort of approximations for the field at a large distance from an edge and away from the GO boundaries.

Improved Physical Theory of Diffraction: Removal of the Grazing Singularity

Abstract: Physical theory of diffraction based on the concept of elementary edge waves [P. Ya. Ufimtsev, Electromagnetics, vol. 11, no. 2, pp. 125-160, 1991] is well suited for analysis of backscattering from perfectly conducting objects with edges. However, it needs to be improved for the investigation of forward scattering, especially in the directions grazing to the edge faces, where it predicts infinite values. The present paper removes this singularity by introducing a new definition for the uniform component of the surface current. This component is defined here as the current induced on the half-plane tangential to the illuminated face of the scattering edge (and to the edge itself). The improved theory of elementary edge waves is developed, which is valid for all scattering directions, including forward scattering

Equivalence between physical optics and aperture integration for radiation from open-ended waveguides

Abstract: The eigen-mode radiation from an open-ended waveguide of arbitrary cross section is considered. The following theorem is demonstrated: the Kirchhoff-Kottler aperture integration for the radiated field is equivalent to the physical-optics (PO) approach applied to the wall currents. This theorem allows one to resort to aperture integration for those structures involving complicated PO integration. On the other hand, based on the same theorem the aperture integration may be reduced to a line integral along the edge of the waveguide for those configurations that allow a simple PO integration. It can also be useful in developing more efficient solutions in the framework of incremental theories.

Singular edge behavior: To impose or not impose—that is the question

Abstract: It has been conjectured that the incorporation of singular edge current behavior may facilitate the numerical solution of scattering problems. This paper will show that special attention is needed to properly incorporate this condition. It is demonstrated that, contrary to common practice, the edge condition is not only a geometry-specific condition, but also is source specific, greatly depending on the amplitude and direction of the incident field. Both analytical and numerical techniques are used to explain the key observations of this paper. ©2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 218–223, 2000.

Improved PO-MM hybrid formulation for scattering from three-dimensional perfectly conducting bodies of arbitrary shape

Abstract: The method of moments (MM) represents a suitable procedure for dealing with electromagnetic scattering problems of arbitrary geometrical shape in the lower frequency range. However, with increasing frequency both computation time and memory requirement often exceed available computer capacities. Therefore a current based hybrid method combining the MM with the physical optics (PO) approximation suitable for three-dimensional perfectly conducting bodies is proposed in this paper. The hybrid formulation allows a substantial reduction of computation time and memory requirement, while the results are in reasonable agreement with those based on an application of the MM alone. Further improvement can be achieved for flat polygonal parts of the scattering body by a heuristic modification of the PO current density taking into account the effects of edges. As opposed to the physical theory of diffraction (PTD), no additional electric and magnetic line currents along the edges are necessary. >

An Iteration-Free MoM Approach Based on Excitation Independent Characteristic Basis Functions for Solving Large Multiscale Electromagnetic Scattering Problems

Abstract: We describe a numerically efficient strategy for solving a linear system of equations arising in the Method of Moments for solving electromagnetic scattering problems. This novel approach, termed as the characteristic basis function method (CBFM), is based on utilizing characteristic basis functions (CBFs)-special functions defined on macro domains (blocks)-that include a relatively large number of conventional sub-domains discretized by using triangular or rectangular patches. Use of these basis functions leads to a significant reduction in the number of unknowns, and results in a substantial size reduction of the MoM matrix; this, in turn, enables us to handle the reduced matrix by using a direct solver, without the need to iterate. In addition, the paper shows that the CBFs can be generated by using a sparse representation of the impedance matrix-resulting in lower computational cost-and that, in contrast to the iterative techniques, multiple excitations can be handled with only a small overhead. Another important attribute of the CBFM is that it is readily parallelized. Numerical results that demonstrate the accuracy and time efficiency of the CBFM for several representative scattering problems are included in the paper.

A generalized diffraction synthesis technique for high performance reflector antennas

Abstract: Stringent requirements on reflector antenna performances in modern applications such as direct broadcast satellite (DBS) communications, radar systems, and radio astronomy have demanded the development of sophisticated synthesis techniques. Presented in the paper is a generalized diffraction synthesis technique for single- and dual-reflector antennas fed by either a single feed or an array feed. High versatility and accuracy are achieved by combining optimization procedures and diffraction analysis such as physical optics (PO) and physical theory of diffraction (PTD). With this technique, one may simultaneously shape the reflector surfaces and adjust the positions, orientations, and excitations of an arbitrarily configured array feed to produce the specified radiation characteristics such as high directivity, contoured patterns, and low sidelobe levels, etc. The shaped reflectors are represented by a set of orthogonal global expansion functions (the Jacobi-Fourier expansion), and are characterized by smooth surfaces, well-defined (superquadric) circumferences, and continuous surface derivatives. The sample applications of contoured beam antenna designs and reflector surface distortion compensation are given to illustrate the effectiveness of this diffraction synthesis technique. >

Computation of the RCS of complex bodies modeled using NURBS surfaces

Abstract: The paper presents the RANURS code (radar cross section-NURBS surfaces) for the analysis of the monostatic radar cross section (RCS) of electrically large complex targets. The geometric representation of the targets is given in terms of parametric surfaces, which allow an excellent fit between the model and the real surface. The parametric surfaces used are NURBS (non-uniform rational B-spline) surfaces. This technique of modeling is used in many industries to represent complex bodies. Most of the CAGD (computer aided geometric design) tools use the NURBS format for modeling, because it can represent complicated objects using limited information. Therefore, an important feature of the code is its compatibility with most of the available CAGD codes, in order to ensure that the entire design process, involving different engineering aspects (structural, mechanical, aerodynamical, electrical, etc.) can be developed with compatible models. The scattered fields are calculated by using the physical optics and the equivalent currents methods (PO+ECM). The following contributions to the RCS are taken into account: reflected field, diffracted field, double-reflected field, and diffracted-reflected field. In addition, a method for determining the hidden parts of the targets is used. The PO+ECM approach is directly applied on the parametric surfaces, and the final expressions of the fields are given as functions of the coefficients of the numerical description of the NURBS patches.

Improvement of the PO-MoM hybrid method by accounting for effects of perfectly conducting wedges

Abstract: A correction of the conventional physical optics (PO) current close-to-perfectly conducting wedges based on an application of the uniform geometrical theory of diffraction (UTD) is presented. This improved PO current is used in a hybrid formulation in combination with the method of moments (MoM) to deal with three-dimensional scattering bodies of arbitrary shape. The accuracy of this hybrid method is demonstrated by some examples. As opposed to an application of the physical theory of diffraction (PTD), only surface current densities and no fictitious electric and magnetic line currents along the edges are involved which allows a uniform treatment of the MoM and the PO region by expressing the surface current density as a superposition of basis functions defined over triangular patches. >